BACKGROUND: Treatment-related side effects are common among women treated for early breast cancer and their effective management is essential to maintain quality of life, ensure treatment adherence, and optimise survival outcomes. This study aimed to investigate patient-reported experiences and preferences about information regarding side effects received during breast cancer care. METHODS: An international multi-stakeholder expert group conducted an online patient survey assessing comprehensiveness, timing, and delivery modality of information regarding treatment-related side effects among patients undergoing primary therapy (surgery, radiation, and [neo]adjuvant chemotherapy) and endocrine therapy for early breast cancer. Descriptive analyses were performed. RESULTS: From June-August 2023, 608 respondents from Brazil, France, Germany, Italy, Japan, and Spain completed the survey: 57.5 % were <
50 years old, and all were or had been on endocrine therapy. Fatigue was the most reported side effect (47.0 % for primary and 42.3 % for endocrine therapy). A variable proportion of patients (14.4%-46.8 % across side effects) reported receiving information only after having experienced the side effect. Up to 43.6 % of respondents reported receiving insufficient or no information on side effects from their healthcare providers. Most patients reported preference for proactive communication from healthcare providers about side effects and prevention strategies. Respondents valued direct interactions with physicians and nurses and capitalised on a relevant role for peer-support, however utility of smartphone and web-based platforms to record and manage symptoms was acknowledged. CONCLUSION: The survey underscores critical needs and offers insight informing the provision of comprehensive and timely information on treatment-related side effects across the cancer survivorship continuum.